This application relates to the use of cold metal transfer techniques to repair internal holding structures, such as the rail or seal grooves on a case for a gas turbine engine.
Gas turbine engines include cases that surround the turbine sections. These cases will have internal holding structures, such as grooves to receive vanes or seals. Over time, the grooves wear, and need to be repaired.
In the prior art, these grooves have been repaired by adding additional material through welding techniques, such as manual tungsten inert gas (“TIG”) welding. The cases are typically out of round and out of flatness when removed for service. Manually welding these cases is time consuming task, and is not ergonomic. Other gas turbine engine cases, such as diffuser and compressor cases, can have similar problems.
A process known as cold metal transfer (“CMT”), has been incorporated into gas metal arc or metal inert gas (“MIG”) welding systems. This process reduces the spatter often associated with MIG welding. This spatter has kept MIG welding from gaining popularity in the aerospace industry. An example of the CMT process has been developed by Fronius Corporation.
The term “cold” has to be understood in terms of a welding process. When compared to a conventional MIG process, CMT is a cold process. Its characteristic feature is alternating hot and relatively cold temperature. This alternating hot and cold treatment occurs by incorporating a welding wire motion into a process control.
The wire moves forward and into a weld pool. A short circuit occurs. As the short circuit happens, the wire is pulled back again. In this way, a weld arc only inputs heat very briefly in the arcing period, after which the thermal input is immediately reduced. In this way, the alternating hot and cold occurs.
The rearward movement of the wire assists weld material droplet detachment during the short circuit. The short circuit is thus controlled and kept small.
CMT has not been utilized in repair applications for gas turbine engine cases.